Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-08-04
2003-08-05
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06601944
ABSTRACT:
This application is based on Japanese Patent Application Nos. 11-227942 (1999) filed Aug. 11, 1999, and 2000-217757 (2000) filed Jul. 18, 2000, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image printing apparatus for printing various kinds of image information in personal computers, word processors, electronic typewriters, facsimiles or the like.
2. Description of the Prior Art
Recently, office automation equipment, such as personal computers and word processors, has come to be used widely in individual households. It is becoming commonplace for the users of this kind of equipment to upload photoprints, process and output images or the like by using input means such as a digital camera and a film scanner.
Under such circumstances, the image printing apparatus, as one of the various output means, is increasingly required to be provided with the ability to output a high-quality image such as the photoprint, and it has been improved in various aspects in order to meet such requirement. At present, a so-called serial-type image printing apparatus designed for obtaining a desired print by scanning a printing medium with a printing head is prevailing mainly due to the printing cost. A means for improving the quality of the image obtainable by the serial-type image printing apparatus is to improve the positioning accuracy of the printing head relative to the printing medium.
In a serial-type image printing apparatus, the printing head is attached to a carriage, and the carriage is moved, for scanning, in a breadthwise direction of the printing medium by a stepping motor. The printing head is driven correspondingly to the timing of the driving operation of the stepping motor to effect the printing operation of the printing head to the printing medium. Is this case, in order to scan the carriage at a constant speed, it is necessary for the stepping motor to be driven with a constant revolution. The amount of revolution of the stepping motor and the scanning movement of the carriage do not necessarily have a one-to-one relationship because of structural factors such as the delay of the rotor relative to the excitation phase of the stepping motor or the vibration of the cogged belt for coupling the stepping motor and the carriage. In other words, driving the printing head correspondingly to the driving revolution of the stepping motor does not necessarily assure the formation of good images.
Therefore, in order to resolve the problem of a decrease in imaging quality caused by the previously mentioned structural factors, it is necessary to detect the absolute position of the carriage, on which the printing head is attached, so that the printing head can be driven correspondingly to the detection signal.
As for the method for detecting the absolute position of the carriage, it is a common practice to read, by means of an optical or magnetic sensor mounted on the carriage, the position of the carriage on the basis of the linear encoder scale, which covers the full stroke of the carriage.
FIG. 12
shows a schematic illustration of the carriage in a conventional image printing apparatus. In this illustration, a guide shaft
104
, for defining the direction of scanning movement of the carriage
102
, slidably passes through a guide bush
103
, which is provided at the rear end of the carriage
102
, whereon a printing head
101
is attached for forming image on a printing medium (not shown). The carriage
102
is made to move for scanning along the guide shaft
104
when the cogged belt (not shown), connected with the carriage
102
, is driven. The linear encoder scale
105
provided in parallel with the guide shaft
104
, consists of a transparent PET (polyethylene terephthalate) web with black scale printed thereon at predetermined intervals. A printed circuit board
106
mounted at the rear end of the carriage
102
is provided not only with various devices, such as a capacitor
107
, for driving the printing head
101
but also with an optical encoder sensor
108
for detecting the position of the carriage
102
by optically reading the scale on the linear encoder scale
105
.
The position of the carriage
102
with respect to the linear encoder scale
105
can be determined accurately by reading the scale printed on the linear encoder scale
105
by using the encoder sensor
108
while the carriage
102
is moving for scanning. Any desired image can be printed on the printing medium by driving the printing head
101
correspondingly to the detection signal.
In the case of the conventional image printing apparatus illustrated in
FIG. 12
, the paper dust produced by the friction occurring during the transfer of the printing medium or the common dust, occurring depending on its location, accumulates on the linear encoder scale
105
and the encoder sensor
108
. Especially, in the case of the ink-jet printer, the ink and the treatment liquid for adjusting the printability of the ink to the printing medium, which are discharged from the printing head, form floating mist to accumulate on the linear encoder scale
105
and the encoder sensor
108
. As a result, during the long use of the image printing apparatus, foreign matters such as previously mentioned paper dust, common dust or the mist adheres to the linear encoder scale
105
, thereby not only making the linear encoder scale
105
hard to be read accurately but also making it difficult to print high-quality image on the printing medium.
When using a magnetic-type encoder as the linear encoder scale
105
, the adhesion of foreign matters such as the paper dust, common dust and mist can be prevented by closely attaching a cover to the linear encoder scale. This type of image printing apparatus is disclosed in Japanese Patent Application Laid-open No. 5-298628 (1993) and U.S. Pat. No. 5,450,106. However, when an optical-type encoder is adopted, if the cover is closely provided with the linear encoder scale, there is the possibility that the linear encoder scale is damaged or contaminated widely by the paper dust, common dust or the mist. And, this can adversely affect the accurate reading by the encoder sensor.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an image printing apparatus capable of printing high-quality images on the printing medium over a long period of time not only by preventing the foreign matters such as the paper dust, common dust or the mist from adhering to the scale or the sensor but also by preventing the linear encoder scale from being damaged.
An image printing apparatus according to the present invention includes means for conveying a printing medium and means for scanning a carriage to move across the direction in which the printing medium is conveyed by the printing medium conveying means, the carriage being attached to a printing head for printing an image on the printing medium, the image printing apparatus comprising:
a scale disposed along the direction of scanning of the carriage by the scanning means,
a sensor for detecting the position of the carriage relative to the scale, the sensor being mounted on the carriage opposite to the scale, and
a cover for covering the sensor and at least a part of the scale adjoining the sensor, the cover being provided with a guide portion for guiding the scale to a predetermined position with respect to the sensor.
According to the present invention, because the image printing apparatus comprises the cover for covering the sensor which is provided with the carriage so that the sensor opposes the scale disposed along the direction of scanning of the carriage, with the cover being provided with a guide portion for guiding the scale to a predetermined position with respect to the sensor, foreign matters such as the paper dust, common dust or the like adheres only on the surface of the cover, preventing them from adhering to the sensor and the scale. The scale is guided to a predetermined position relative to the sensor by the guide portion o
Fitzpatrick, Cella, Harper & Scinot
Tran Huan
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